Apparatus for setting proportional margins based upon the width of a scanned sheet of paper

Abstract

In a typewriter environment, a carrier mounted sensor for calculating the width of a sheet of paper on the platen and for thereafter setting-up proportional margins for that sheet of paper. In addition to supporting the sensor, the carrier supports the printhead and associated apparatus for detecting the position of the carrier relative to the platen at each escapement position of the carrier. The sensor starts its scan at the extreme left position of the carrier and senses the left edge of the paper at a transition from dark (the platen surface)-to-light (the sheet of paper). This transition point is detected and stored. The carrier continues its rightward scan and the right edge of the sheet of paper signals a transition from light-to-dark. This position is detected and stored. The carrier and sensor continue scanning to the right for a specific distance to eliminate errors that are caused by dark areas on the paper that prematurely trigger light-to-dark transitions. At the end of the scan, the recorded distances yield the width of the sheet of paper and from this recorded width margins equal to a certain proportion of the total recorded width of the sheet of paper are set.

What is claimed is: 
     
       1. An automatic proportional margin setting apparatus for a typewriter including: a platen for supporting a sheet of paper thereon;   a carrier mounted for relative movement with respect to said platen in a substantially parallel path;   printing means mounted on said carrier for printing indicia on the sheet of paper supported on said platen;   sensing means mounted on said carrier for defining the location of the left and right edges of the sheet of paper supported on said platen;   means responsive to the defined location of the left and right edges of said sheet of paper for determining the width of said sheet of paper;   margin setting means for defining margin locations in accordance with the defined edge locations and in accordance with a predetermined proportional distance; said margin setting means comprising means for establishing a fraction of said width as said proportional distance of said width, and means for combining said proportional distance with said right and left edge locations for determining the margin locations.   
     
     
       2. The automatic proportional margin setting apparatus of claim 1 wherein said sensing means is comprised of an optical paper scanner for detecting the location of the left and right edges of the sheet of paper supported on said platen and further comprising: a grating with grating indicia thereon corresponding to every print position along the length of said platen;   a grating strip scanner for detecting the location of said printing means relative to said platen at every print position, said margin setting means including means for locating said margin in setting proportional margins for the sheet of paper supported on said platen by locating the position of said paper sheet edges relative to said carrier.   
     
     
       3. The automatic proportional margin setting apparatus of claim 2 including drive means for driving said carrier in said path wherein said optical paper scanner traverses the length of said platen and the sheet of paper supported thereon and senses transitions between said platen and the sheet of paper to define the locations of the left and right edges of the sheet of paper. 
     
     
       4. The automatic proportional margin setting apparatus of claim 3 wherein said optical paper scanner includes circuit means for providing pulse output upon the transitions occurring between said platen and the sheet of paper supported thereon. 
     
     
       5. The automatic proportional margin setting apparatus of claim 4 further including at least two latches being triggered by a pulse from said optical paper scanner at every transition between said platen and the sheet of paper, and at least two registers for storing the transition information output from said two latches; the transition information corresponding to the locations of the left and right edges of the sheet of paper. 
     
     
       6. The automatic proportional margin setting apparatus of claim 5 further including a third latch means and a gate means for clearing the latch of said at least two latches and the register of said at least two registers, said cleared register being the register that records and stores the transition information pertaining to the location of the right edge of the sheet of paper when a transition is detected and said cleared latch being the latch that is triggered by dark material on the sheet of paper and not by the platen at the right edge of the sheet of paper. 
     
     
       7. The automatic proportional margin setting apparatus of claim 5 further including right edge switch means located at the extreme right end of said platen said switch means being activated when said carrier reaches an extreme right position and the location of the right edge of the sheet of paper is not detected by said paper scanner; said switch means, when activated, providing a signal output indicating that the location of the right edge switch means is the location of the right edge of the sheet of paper. 
     
     
       8. The automatic proportional margin setting apparatus of claim 1 wherein said means for determining the width of said sheet of paper includes means for subtracting the defined location corresponding to the left edge of the sheet of paper from the defined location corresponding to the right edge of the sheet of paper to yield the width of the sheet of paper. 
     
     
       9. The automatic proportional margin setting apparatus of claim 8 wherein said means for subtracting comprises a two's complement circuit and an adder. 
     
     
       10. The automatic proportional margin setting apparatus of claim 8 wherein said margin setting means further includes a programmable means for taking a predetermined proportion of the width of the sheet of paper for use as margins. 
     
     
       11. The automatic proportional margin setting apparatus of claim 10 wherein said programmable proportional margin setting means is a divide-by-eight circuit. 
     
     
       12. The automatic proportional margin setting apparatus of claim 10 further including a maximum margin setting means for setting a maximum limit on the width of margins for the sheet of paper. 
     
     
       13. The automatic proportional margin setting apparatus of claim 12 wherein said means for establishing a fraction of said width includes comparator means for comparing the margin value from said programmable proportional margin setting means with the margin value from said maximum margin setting means and for accepting the margin value having the smallest width as the margin width for the sheet of paper. 
     
     
       14. The automatic proportional margin setting apparatus of claim 13 wherein said means for combining said proportional distance with said right and left edge locations includes means for adding the margin width to the location of the left edge of the sheet of paper and means for subtracting the margin width from the location of the right edge of the sheet of paper to yield both the left and right margins for the sheet of paper. 
     
     
       15. An automatic proportional margin setting apparatus for a typewriter including: a platen for supporting a sheet of paper thereon;   printing means for printing indicia on the sheet of paper supported on said platen;   sensing means for defining the location of the left and right edges of said sheet of paper supported on said platen; said sensing means including a first scanner for detecting the location of said printing means at every print position and a second scanner for sensing the location of the left and right edges of said sheet of paper on said platen; said second scanner sensing transitions between said platen and the sheet of paper to locate the left and right edges of the sheet of paper;   latch means triggered by every transition between said platen and the sheet of paper;   means for storing the transition information from said latch means;   means for subtracting the transition information corresponding to the left edge of the sheet of paper from the transition information corresponding to the right edge of the sheet of paper to yield the width of the sheet of paper;   programmable proportional margin setting means for determining a predetermined proportion of the width of the sheet of paper for use as margins; and   means for adding the predetermined proportional margin width to the location of the left edge of the sheet of paper and means for subtracting the predetermined proportional margin width from the location of the right edge of the sheet of paper to yield both the left and right margins for the sheet of paper.